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Unformatted text preview: BICD 130 Embryos, Genes, and Development Regional expression of homeotic (Hox) genes defines segment identity
Hox genes all encode homeodomain transcription factors Loss of Ubx function in T3 yields a four-winged fly
Ed Lewis Misexpression of Antennapedia in the head causes an antenna-to-leg transformation Nobel Prizes in Developmental Biology
Christiane Nusslein-Volhard Eric Wieschaus Ed Lewis 1995 The cortical rotation establishes the D/V axis of the frog embryo Artificial cytoplasmic rotation induces a second blastopore and a second dorsal axis Twinned tadpoles resulting from artificial cytoplasmic rotation Formation of the dorsal axis requires gray crescent cytoplasm (Hans Spemann) The Spemann Organizer Hans Spemann and Hilde Mangold The Spemann Organizer induces a complete second axis Nobel Prizes in Developmental Biology
Hans Spemann 1935 Hensen s node is the avian equivalent of the amphibian Organizer otx2 (head) hoxb1 (trunk) Vegetal endoderm cells induce the formation of mesoderm in the amphibian embryo The Nieuwkoop center: Dorsal vegetal blastomeres have axis-inducing activity Model: The Nieuwkoop center induces dorsal mesoderm and the Organizer Model for the creation of the Nieuwkoop center The Wnt pathway: Disheveled promotes the accumulation of catenin in the nucleus Model: The cortical rotation redistributes Dsh protein to the future dorsal side of the embryo Model: Dorsally localized Dsh protein promotes the nuclear accumulation of catenin on the dorsal side
dorsal ventral -catenin A second dorsal axis is formed by injection of dominant-negative GSK-3 into both blastomeres of a 2cell embryo Model: Control of dorsal- and Organizerspecific gene expression transcription factor transcription factor Injection of goosecoid mRNA into ventral vegetal blastomeres induces a secondary blastopore and a second dorsal axis The mesoderm is patterned in the D/V axis How the Organizer Works, Part I: It is a source of diffusible inhibitors of the powerful ventralizing signal BMP4 BMP Inhibitors in Amphibian Axis Formation
Noggin Chordin Nodal-related 3 Follistatin Rescue of dorsal structures by Noggin in UVirradiated 1-cell Xenopus embryos
Increasing dose of noggin mRNA noggin and chordin mRNAs are expressed in Organizer tissue from gastrulation onwards noggin chordin Pharyngeal endoderm and prechordal mesoderm are required for head formation and are the most anterior portions of the Organizer How the Organizer Works, Part II: It is a source of diffusible inhibitors of ventralizing Wnt signals Formation of anterior head structures requires inhibition of the ventralizing signal Xwnt8 Wnt Inhibitors in Amphibian Head Formation
Cerberus Frzb Dickkopf Action of Wnt inhibitors made by the Organizer A soluble form of the Frizzled receptor acts as an inhibitor of Xwnt8 Injection of cerberus mRNA into a single ventral vegetal blastomere at 32-cell stage induces ectopic head structures in the tadpole Summary of locations and actions of inhibitory factors made by Organizer tissue ...
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